In the Herbology classroom, walk into the room with four flower pots on a table. 
You will see a bucket hanging on the ceiling above the dancing water can. Use 
Wingardium Leviosa on the bucket and let it hover over each of the pots. It will 
pour dirt into them. Next, use Wingardium Leviosa on the water can. Hover it 
over each dirt-filled pot until it spews water on them. Spikey-plants will grow. 
You will receive Discovery Points. Then, go to the entrance of the Herbology 
room. Walk forward into the dead-end hallway directly in front of the door in 
the classroom. You will see a rope hanging up in a corner. Use Accio, and it 
will air out the room and give you Discovery Points.